Lead and strontium isotopes as palaeodietary indicators in the Western Cape of South Africa

Mari Scott; Petrus le Roux; Judith Sealy; Robyn Pickering

doi:10.17159/sajs.2020/6700

Authors

Mari Scott Department of Geological Sciences, University of Cape Town, Cape Town, South Africa
Petrus le Roux Department of Geological Sciences, University of Cape Town, Cape Town, South Africa https://orcid.org/0000-0002-5930-4995
Judith Sealy Department of Archaeology, University of Cape Town, Cape Town, South Africa https://orcid.org/0000-0001-5071-8211
Robyn Pickering 1. Department of Geological Sciences, University of Cape Town, Cape Town, South Africa; 2. Human Evolution Research Institute, University of Cape Town, Cape Town, South Africa https://orcid.org/0000-0002-2663-7574

DOI:

https://doi.org/10.17159/sajs.2020/6700

Keywords:

Sr isotopes, Pb isotopes, palaeodiet, archaeology, southwestern South Africa

Abstract

We analysed the isotopic compositions of bioavailable strontium (Sr) and lead (Pb) in 47 samples of animals and plants derived from the various geological substrates of southwestern South Africa, to explore the utility of these isotope systems as dietary tracers. Measurements were made using high-resolution multi-collector inductively-coupled-plasma mass spectrometry (MC-ICP-MS). ⁸⁷Sr/⁸⁶Sr could efficiently discriminate between geologically recent sediments of marine origin in near-coastal environments and older geologies further inland. However, ⁸⁷Sr/⁸⁶Sr was not able to distinguish between the Cape Granite Suite and the Cape System (Table Mountain sandstones), whereas Pb isotopes could, demonstrating the utility of this hitherto underused isotope system. Bioavailable ⁸⁷Sr/⁸⁶Sr in near-coastal terrestrial environments is influenced by marine input, whereas Pb isotopic ratios are not, because of low concentrations of Pb in seawater. There is considerable potential to use Pb isotopes as a dietary and palaeodietary tracer in near-coastal systems in fields as diverse as archaeology, palaeontology, wildlife ecology and forensics.

Significance:

This study is the first investigation of the potential of Pb isotopes as a dietary tracer in southwestern South Africa.
Pb isotopes are a valuable dietary tracer; used in combination with ⁸⁷Sr/⁸⁶Sr, they can extend our knowledge of landscape usage in coastal-marine environments.
Pb isotopes have also shown to be useful in samples from the 1980s, collected during the time when leaded petrol was in use in South Africa; however, these samples were from remote areas with low motor vehicle emissions.